The present invention relates generally to an exposure apparatus, and more particularly to an exposure apparatus for exposing an object, such as a single crystal substrate for a semiconductor wafer and a glass plate for a liquid crystal display (“LCD”).
Recent demands on smaller and thinner profile electronic devices have increasingly required finer semiconductor devices to be mounted on these electronic devices. For example, the mask-pattern design rule requires a formation of an image with a size of a line and space (“L & S”) of less than 0.1 μm in an extensive area. A transfer to circuit patterns of less than 80 nm is expected in the near future. L & S denotes an image projected onto a wafer with equal line and space widths in exposure, and serves as an index of exposure resolution.
A projection exposure apparatus as a typical exposure apparatus for manufacturing semiconductor devices includes a projection optical system for exposing a pattern on a mask (reticle) onto a wafer. Effective to higher resolution are shortening of a wavelength of a light source, and increasing of a numerical aperture (“NA”) of the projection optical system as well as maintaining aberrations in the projection optical system to be extremely small.
The projection optical system houses, in a lens or mirror barrel (“lens barrel”), an imaging optical system for imaging diffracted light from a reticle. When the imaging optical system has a lens that decenters from the optical axis, the light that should form an image at one point does not converge on one point, causing aberrations, such as a partial defocus, a distortion, and a curvature of field. To correct the aberrations, the projection optical system incorporates an aberration correcting optical system with the lens barrel. The aberration correcting optical system inclines a non-imaging lens that inclines (or has an tilt angle) relative to the optical axis according to the aberrational amount. The aberration correcting optical system determines a position and an orientation (or an tilt angle) of the lens according to the aberrational amount, and is configured to fix the lens as determined.
However, the above incorporation of the above aberration correcting optical system fixes the inclination of the lens to the optical axis, and therefore disadvantageously cannot correct aberrations, such as dynamically variable partial defocuses, distortions and curvatures of field, caused by a deformations (expansions, etc.) of the lenses in the imaging optical system due to environmental variances and exposure heats, such as temperature changes. In addition, the lenses in the imaging optical system are made rotated about or moved along the optical axis so as to correct the astigmatism, aspect ratio, etc. This rotations and/or movements also result in decentering from the optical axis. Insufficient corrections of the aberrations, such as the partial defocuses, distortions and curvatures of field, do not provide desired resolution.
Due to inevitable incorporation errors, it is significantly difficult to incorporate the aberration correcting optical system into the lens barrel while maintaining the lens's inclination determined and fixed by the aberrational amount. Moreover, it is bad operability to change the inclination of the lens in the aberration correcting optical system by taking out the aberration correcting optical system from the lens barrel in the projection optical system, and changing the lens's inclination, followed by reincorporation.